Dikshi Gupta

RNA interference therapeutics for cancer: Challenges and opportunities (Review)

RNA interference (RNAi) is a sequence-specific, post-transcriptional gene silencing mechanism in animals and plants, which is mediated by double-stranded RNA (dsRNA). There has recently been an increasing interest in harnessing the gene silencing activity of dsRNA to develop novel drugs for the treatment of various diseases, such as cancer, neurological disorders, age-related macular degeneration and viral infections. Small interfering RNA (siRNA)-based drugs have distinct advantages over conventional small molecule or protein-based drugs, including high specificity, higher potency and reduced toxicity. However, there are several technical obstacles to overcome before siRNA-based drugs reach the clinic. Delivery of siRNA to the target tissues and stability in the serum remain a major challenge and are the main focus of current research and development efforts. This review focused primarily on the progress made in developing RNAi as therapeutics for cancer and the challenges associated with its clinical development. Use of ligands recognizing cell-specific receptors to achieve tumor-specific delivery of siRNA, methods for enhanced siRNA delivery, improving the bioavailability and pharmacokinetic properties of siRNA and reducing the off-target effects and non-specific gene silencing are discussed in the light of current evidence.

Cloning, stable expression of human phosphodiesterase 7A and development of an assay for screening of PDE7 selective inhibitors

Phosphodiesterases (PDEs) constitute a superfamily of enzymes that plays an important role in signal transduction by catalysing the hydrolysis of cAMP and cGMP. cDNA encoding PDE7A1 subtype was cloned and a stable recombinant HEK 293 cell line expressing high levels of PDE7A1 was generated. Transient transfection of pCRE-Luc plasmid, harboring luciferase reporter gene into the stable recombinant cell line and subsequent treatment with PDE7 inhibitor, resulted in a dose-dependent increase in luciferase activity. This method provides a simple and sensitive cell-based assay for screening of PDE7 selective inhibitors for the treatment of T cell mediated diseases.

Development of a cell-based assay for screening of phosphodiesterase 10A (PDE10A) inhibitors using a stable recombinant HEK-293 cell line expressing high levels of PDE10A.

cDNA encoding PDE10A (phosphodiesterase 10A) was cloned and a stable recombinant HEK‐293 (human embryonic kidney‐293) cell line expressing high levels of PDE10A was generated. Transient transfection of pCRE‐Luc plasmid, harbouring the luciferase reporter gene under the control of CRE (cAMP‐response element)‐binding sequence, into the stable recombinant cell line, followed by treatment with PDE10 inhibitor, resulted in a dose‐dependent increase in luciferase activity. This method provides a simple and sensitive cell‐based assay for screening of PDE10 inhibitors for development of novel therapeutics for the treatment of neurological disorders.

Molecular cloning, stable expression and cellular localization of human α1-adrenergic receptor subtypes: effect of charcoal/dextran treated serum on expression and localization of α1D-adrenergic receptor

The cDNAs encoding for three subtypes of adrenergic receptors, α1A-, α1B- and α1D-ARs, were cloned and expressed in HEK 293 cells. Expression of α1A- and α1B-AR subtypes in HEK 293 cells was stable even with increased passages but that of α1D-AR was not. Cellular localization studies using immunofluorescence and flow cytometry revealed that expression of α1A- and α1B-ARs was primarily localized on the cell membrane whereas expression of α1D-AR was␣predominantly intracellular. Our studies clearly demonstrated that the culturing of the recombinant cell lines expressing α1D-AR in charcoal/dextran treated fetal bovine serum (FBS) resulted in targeting of α1D-AR to the cell membrane and thus, significantly improving its stability and availability for ligand binding studies.

High level stable expression of pharmacologically active human M1-M5 muscarinic receptor subtypes in mammalian cells.

AbstractcDNAs encoding for five mAChR subtypes (M1–M5) were cloned under different promoters in various eukaryotic vectors and each subtype was expressed in different mammalian cell lines. CHO-K1 cell line was the best for generating stable cell lines expressing muscarinic receptors. Immunofluorescence and flow cytometry revealed that expression of M1–M5 was primarily localized on the cell membrane. Western blotting and radio-ligand binding studies revealed that expression of each receptor was stable at higher passages.

Ratiometric Ca+2 measurement in human recombinant muscarinic receptor subtypes using the Flexstation scanning fluorometer

In modern drug discovery, numerous assay formats are available to screen and quantitate receptor-ligand interactions. Radioactive assays are “gold standard” because they are fast, easy, and reproducible; however, they are hazardous, produce radioactive waste, require special lab conditions, and are expensive on a large scale. Thus, it provides a lot of importance to the “mix & measure” assays that have an optical readout. Fluorescence techniques are likely to be among the most important detection approaches used for high throughput screening due to their high sensitivity and amenability to automation. The aim of the present study was to determine the functional antagonistic affinities of standard muscarinic antagonists in CHO cells over expressing m1, m3, and m5 receptors and to compare them with the respective binding affinities. This study was further extended to elucidate that Ca+2 measurement assays can serve as a functional screening tool for GPCRs. For this purpose, standard muscarinic receptor antagonists, namely, tolterodine, oxybutynin, and atropine were used. We determined and compard the IC50 values of these three standard inhibitors in fura 2 AM loaded m1, m3, and m5 overexpressing CHO cells and in radioligand binding assay. Both the assays exhibited comparable rank order potencies of the standard inhibitors. This study suggests that Ca+2 mobilization assays can be an alternate to radioligand binding assays.

Functional screening of adrenergic receptors by measuring intracellular calcium using the FlexStation scanning fluorimeter.

In this study we test whether functional screening of compounds to adrenergic G protein-coupled receptors (GPCRs) would provide data that correlated significantly with radiolabeled binding data, thereby permitting researchers to replace expensive radioligand-binding experiments with non-radioactive screening. An increase in intracellular calcium levels represents an important second messenger signal for several recombinant GPCRs. In this study, we describe the affinities of three alpha adrenoceptor antagonists (terazosin, tamsulosin and alfuzosin), determined by monitoring the changes in intracellular calcium levels and comparing them with their radioligand-binding affinities. In addition to determining the functional affinities of the three alpha adrenoceptor antagonists, we evaluate their binding at two alpha adrenoceptor subtypes and optimized the assay for high-throughput screening.

Experimental bovine rotavirus-A (RV-A)infection causes intestinal and extra-intestinal pathology in suckling mice

We describe here the intestinal and extra-intestinal spread of the species A rotavirus (RV-A) and associated lesions thereof in Swiss albino suckling mice pups, inoculated with a bovine-origin RV-A strain. In total, 35 suckling pups were used, wherein 20 pups received cell culture isolated RV-A @ 160 μL (TCID50/ml, 5 × 106.5) per pup [oral 80 μL and intra peritoneal (IP) 80 μL] and served as an infected group, while 15 pups were kept in the control group and inoculated the same volume of phosphate buffered saline (PBS) of neutral pH orally and IP. Four pups from the infected group and 3 from control group were sacrificed at 3, 5, 7, 9 and 12 day post infection (DPI). Of note, infected pups exhibited signs of dullness and restlessness till 5DPI, but none showed diarrhea at any point of time. No appreciable gross lesions were evident in any of the organs, except for mild congestion of the small intestine and yellowish catarrhal smearing over the luminal surface. However, light microscopic lesions in hematoxylin and eosin (H&E) stained sections of jejunum and ileum revealed vacuolation and pyknosis of nuclei of the mature enterocytes, their lysis and detachment, constriction and detachment of villi, mild mononuclear cells (MNCs) infiltration in the lamina propria and mildcell depletion of Peyers patches and mesenteric lymph nodes (MLN). The extra-intestinal lesions of the cellular degeneration and mild MNCs infiltration were identified in the liver and kidneys from 3 to 7 DPI, but no lesion was seen in the brain. Interstitial thickening with MNCs of lung parenchyma was visible from 3 to 7 DPI. The lesions in the intestine, lymphoid tissues and lungs resolved after 7 DPI. The presence of viral nucleic acid was seen in the intestinal contents from 3 to 5 DPI by using a RV-A specific reverse-transcription polymerase chain reaction (RT-PCR), while in the MLNs and the lungs it could be detected till 5 DPI by both the RT-PCR and direct fluorescent antigen test (dFAT). However, liver, spleen and brain were tested negative for the presence of RV-A by any of these tests. Nonetheless, the persistence of the RV-A was seen in the MLNs even after the absence of virus from the small intestines. Findings here conclusively indicates that heterologous host origin RV-A has an affinity not only to the intestine but also to extra-intestinal tissues like MLNs and lung tissues.

Etiopathology of intestinal affections in bovine calves

A variety of infectious agents are implicated in calf diarrhoea, and co-infection of multiple pathogens is not uncommon in diarrheic calves. Forty carcasses of bovine calves having history of diarrhoea were necropsied and the samples of intestine, lung, liver, kidney, heart and lymph nodes were collected in 10% neutral buffered formalin for histopathology and in -20°C for molecular diagnosis. Lesions of enteritis were observed histopathologically, and rotavirus was predominantly associated with enteritis along with other concomitant infections viz. pasteurellosis, FMD, parasites, aflatoxicosis and septicaemia etc. In most of the cases, the aetiologies were confirmed by PCR (rotavirus and FMD virus), bacterial culture (bacterial enteritis) and by pathological lesions in the intestines and other organs. It was observed that rotavirus enteritis usually found associatedalong with concomitant infections.